Field of the Invention
The invention relates to a measuring tube for a magneto-inductive flow measuring system, wherein the flow measuring system has the measuring tube for the flow of an electrically conductive medium and a magnetic field generator for generating a, preferably alternating, magnetic field running at least also perpendicular to the longitudinal axis of the measuring tube, at least two measuring electrodes tapping the measuring voltage induced in the electrically conductive medium, preferably in contact with the medium and preferably an evaluation unit, wherein the measuring electrodes have accessible measuring contacts on the outside of the measuring tube and the measuring tube with the measuring electrodes forming a first functional unit and counter contacts corresponding to the measuring contacts of the measuring electrodes, the magnetic field generator and the evaluation unit (insofar such is present) forming a second functional unit and wherein the counter contacts, the magnetic field generator and the evaluation unit (insofar such is present) are provided in a measuring system housing.
Description of Related Art
Magneto-inductive flow-measuring systems have been known extensively for decades in the prior art. Reference is made, as an example, to the citation “Technische Durchflussmessung” from Dr.-Ing. K. W. Bonfig, 3rd Edition, Vulkan-Verlag Essen, 2002, pages 123 to 167 and to the citation “Grundlagen Magnetisch-Induktive Durchflussmessung” from Dipl.-Ing. Friedrich Hoffmann, 3rd Edition, 2003, publication of the company KROHNE Messtechnik GmbH & Co. KG.
The principle of a magneto-inductive flow-measuring system for flow measurement of a flowing medium goes back to Faraday, who, in 1832, suggested using the principle of electromagnetic induction in the measurement of flow rates of an electrically conductive medium.
According to Faraday's law of induction, an electrical field intensity develops perpendicular to the direction of flow of the medium in a flowing, electrically conductive medium interfused by a magnetic field and perpendicular to the magnetic field. Faraday's law of induction is utilized in magneto-inductive flow-measuring systems in that a temporally-alternating magnetic field is usually generated during measurement by means of a magnetic field generator, which usually has at least one magnetic field coil and the magnetic field at least partially interfuses the electrically conductive medium flowing through the measuring tube. Thereby, the generated magnetic field has at least one component perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
As stated above, the at least one magnetic field generator “for generating a magnetic field running at least also perpendicular to the longitudinal axis of the measuring tube” belongs to the magneto-inductive flow-measuring system, then it is indicated here that the magnetic field is namely preferable perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium, but it is sufficient that one component of the magnetic field runs perpendicular to the longitudinal axis of the measuring tube or perpendicular to the direction of flow of the medium.
In the introduction, it is also stated that the magnetic field generator is intended for generating a, preferably alternating, magnetic field. This expresses that it is not important for the teaching of the invention—in respect to its origin, to its objects and to meeting these objects—that it is an alternating magnetic field, even when magneto-inductive flow-measuring systems predominately have magnetic field generators that generate an alternating magnetic field.
It is also mentioned in the introduction that at least two measuring electrodes, preferably in contact with the medium, tapping the measuring voltage induced in the electrically conductive medium belong to the magneto-inductive flow-measuring systems of the type being discussed here. Preferably, the virtual connection line of the two measuring electrodes runs at least essentially perpendicular to the direction of the measuring tube perpendicular to the longitudinal axis of the magnetic field interfusing the measuring tube. In particular, the measuring electrodes can be provided in such a manner that their virtual connection line actually—more or less—runs perpendicular to the longitudinal axis of the magnetic field interfusing the measuring tube.
Finally, it is described in the introduction that the measuring electrodes are such that they can be in contact with the medium. Effectively, of course, the electrical field intensity generated by induction in flowing, electrically conductive medium can be tapped by measuring electrodes that are in direct, i.e., galvanic, contact to the medium as a measuring voltage. However, there are magneto-inductive flow-measuring systems, in which the measuring voltage is not tapped by measuring electrodes that have direct, i.e., galvanic, contact to the medium, but rather the measuring voltage is capacitively determined.
Two different designs of magneto-inductive flow-measuring systems are possible, namely a first design, in which both functional units, i.e., the measuring tube on the one hand and the magnetic field generator on the other hand, are separate components that result in a functional magneto-inductive flow-measuring system when first brought together and a second design, in which the two functional units, i.e., the measuring tube and the magnetic field generator are already brought together in-factory, i.e., components made functional in-factory to result in an already functional magneto-inductive flow-measuring system from the factory.
In the following, only the first design of a magneto-inductive flow-measuring system is described, i.e., the design in which the measuring tube, on the one hand, and the magnetic field generator, on the other hand, are initially separate components that result in a functional magneto-inductive flow-measuring system when they are brought into function with one another. What is described in the following, however, is easily applicable for the second design of magneto-inductive flow-measuring systems, in which both functional units, the measuring tube and the magnetic field generator, are already brought into function with one another in-factory, i.e., components of an already functional magneto-inductive flow-measuring system from the factory.
As an example, reference is made to known magneto-inductive flowmeters from the prior art in German Patent DE 692 32 633 C2, German Patent Application DE 199 07 864 A1 which corresponds to U.S. Pat. No. 6,453,754 B1, German Patent Application DE 100 64 738 B4 which corresponds to U.S. Pat. No. 6,564,612 B2, German Patent Application DE 102 43 748 A1 which corresponds to U.S. Pat. No. 6,804,613 B2, German Patent Application DE 10 2008 005 258 A1 which corresponds to U.S. Pat. No. 7,971,493 B2 and German Patent Application DE 10 2011 112 703 A1 which corresponds to U.S. Patent Application Publication 2012/0066301 A1 as well as European Patent Application EP 0 704 682 A1 and European Patent Application EP 0 834 057 A1 which corresponds to U.S. Pat. No. 6,092,428.
Normally, a magnetic field coil belongs to the magnetic field generator in magneto-inductive flow-measuring systems of the type being discussed here. As a rule, this magnetic field coil has a coil core and two pole shoes are adjacent to the coil core on both sides. The coil core and the pole shoes usually consist of magnetic, conductive material, i.e., of material having a large permeability, and the pole shoes extend beyond the measuring tube on both sides. Thus, the coil core, the poles shoes adjacent to both sides of the coil core and the air gap formed between the pole shoes, in which the measuring tube is located—in the functional state—belong to the magnetic circuit, which is important and necessary for the functioning of the magneto-inductive flow-measuring system being discussed here.
As described in detail, the longitudinal axis of the measuring tube, the direction of the magnetic field and the virtual connection line of the two measuring electrodes form a right-angled tripod. If the longitudinal axis is the X-axis, the direction of the magnetic field the Y-axis, then the virtual connection line of the two measuring electrodes is the Z-axis of the right-angled tripod; the virtual connection line of the two measuring electrodes thus runs perpendicular to the longitudinal axis of the measuring tube as well as perpendicular to the direction of the magnetic field.